A four-wheeled buggy, for example, is known as a type of saddle riding vehicle. The four-wheeled buggy is constructed such that front wheels are steered through a steering mechanism including a handlebar.
In a vehicle having a steering wheel, which has a relatively heavy weight, the speed at which the front wheels are steered is reduced relative to a steering angle on the steering wheel using a predetermined gear ratio, thus providing power assistance for steering the front wheels. A lightweight vehicle, such as the four-wheeled buggy, on the other hand, does not need power assistance for steering the front wheels through a speed reduction by a gear ratio. A lightweight vehicle only requires a relatively light input for steering. Further, a handlebar is more suitable in terms of a vehicular concept with the lightweight vehicle. The lightweight vehicle therefore incorporates the handlebar.
There is nonetheless a need for lighter steering effort to achieve even greater comfort.
To achieve even greater comfort, an electric power steering apparatus is proposed that is incorporated for assisting the steering effort. It is proposed, for example, that such an electric power steering apparatus be inserted between an upper support portion of a steering shaft for supporting an upper portion side of the steering shaft and a lower support portion of the steering shaft for supporting a lower portion side of the steering shaft. The electric power steering apparatus is supported by an upper portion side frame pipe.
In this electric power steering apparatus, an input shaft and an output shaft, each being rotatably journaled, are connected elastically through a torsion bar. The amount of torque is detected based on an amount of torsion of the torsion bar. A gear in mesh with the output shaft is driven by an electric motor based on the amount of torque and the like, thereby assisting the steering effort. See, for example, Japanese Patent No. 2663454 (Page 2, FIG. 1).
The vehicle having a handlebar, such as the four-wheeled buggy, very often runs on a rough road, such as a sandy road, a muddy road, a green field, and the like. Different parts of a vehicle body of such a vehicle therefore tend to be contaminated with mud, dust, rainwater, or the like.
The aforementioned electric power steering apparatus is no exception and is contaminated with mud, dust, rainwater, or the like. One of the parts susceptible to this contamination problem and requiring a solution to the problem is a torque sensor for detecting the amount of torque.
The power steering apparatus has a number of projections and recessed surfaces, on which mud, dust, and other contaminants are more likely to be deposited. There is therefore a need for a structure that can reduce, as much as feasible, the number of projections and recessed surfaces.
Conventionally, a vehicle having a handlebar includes an electric power steering apparatus for enhanced comfort. However, in a compact vehicle such as the four-wheeled buggy, there is a limit in space for mounting the steering power assist apparatus. Therefore, there is a need for a compact apparatus.